Stroke V Stroke Power Calculation

[old] bbsportz · Post by **[old] bbsportz** » May 16th, 2005, 1:33 am

Does anyone know the specific equation used in the PM3 to determine the POWER value expressed at the end of each drive phase. MarkA and MarkO

[old] jamesg · Post by **[old] jamesg** » May 16th, 2005, 4:49 am

My guess is that the PM system derives our power input from the behaviour of the flywheel, by measuring flywheel speed at release; flywheel speed at catch; instants of release, catch and next release. The basic idea is that the work done on the air by the flywheel (calculated from its behaviour) = the work we put in. Using this idea the calculation of our power input is straightforward engineering. PM shows it in Watts. Speed and pace etc are derived from the Power input, using W=kV^3, where V is the "speed" in m/s. k=2.8 if I remember right, and appears to be selected so that the values of V are similar to a boat's speed and a 2k doesn't take ½h nor 20 seconds. The cube function is unfortunately a part of reality: to go twice as fast you have to work eight times as hard.

[old] c2scott · Post by **[old] c2scott** » May 16th, 2005, 8:52 am

<table border='0' align='center' width='95%' cellpadding='3' cellspacing='1'><tr><td><div class='genmed'>QUOTE(bbsportz @ May 16 2005, 12:33 AM)</div></td></tr><tr><td class='quote'>Does anyone know the specific equation used in the PM3 to determine the POWER value expressed at the end of each drive phase. MarkA and MarkO </td></tr></table> The formulas used are: Power (watts) = 2.80 / Pace (sec/meter)³ or Power = 2.80 * Velocity (meters/sec)³ You may also reference: "The Physics of Ergometers" on the web at <a href='http://www.atm.ox.ac.uk/rowing/physics/ ... l#section1' target='_blank'>The Physics of Ergometers</a> and <a href='http://www.atm.ox.ac.uk/rowing/physics/' target='_blank'>FAQ: Physics of Rowing</a> Hope this helps. -- Scott

[old] mlyons · Post by **[old] mlyons** » May 16th, 2005, 1:56 pm

<table border='0' align='center' width='95%' cellpadding='3' cellspacing='1'><tr><td><div class='genmed'>QUOTE(c2scott @ May 16 2005, 07:52 AM)</div></td></tr><tr><td class='quote'><table border='0' align='center' width='95%' cellpadding='3' cellspacing='1'><tr><td><div class='genmed'>QUOTE(bbsportz @ May 16 2005, 12:33 AM)</div></td></tr><tr><td class='quote'>Does anyone know the specific equation used in the PM3 to determine the POWER value expressed at the end of each drive phase. MarkA and MarkO </td></tr></table> The formulas used are: Power (watts) = 2.80 / Pace (sec/meter)³ or Power = 2.80 * Velocity (meters/sec)³ You may also reference: "The Physics of Ergometers" on the web at <a href='http://www.atm.ox.ac.uk/rowing/physics/ ... l#section1' target='_blank'>The Physics of Ergometers</a> and <a href='http://www.atm.ox.ac.uk/rowing/physics/' target='_blank'>FAQ: Physics of Rowing</a> Hope this helps. -- Scott </td></tr></table> Appendix B of the SDK documentation defines this relationship as well calories vs. pace. Mark

[old] bbsportz · Post by **[old] bbsportz** » May 16th, 2005, 9:39 pm

Our interpretation of Anu Dudhia's and Marinus van Holst's site is similar to the one that jamesg responded with. Marinus van Holst, "Behind the Ergometer Display" <a href='http://home.hccnet.nl/m.holst/ErgoDisp.html' target='_blank'>http://home.hccnet.nl/m.holst/ErgoDisp.html</a> These basic engineering concepts have been applied to sports science issues over the past 40years. Do a google search on "Di Prampero energetics" and you will get responses on research publications that cover swimming, running, rowing, paddling, and cycling on the earth and the moon. In addition to the mechanical energetics equations these works include equations that take into account the chemical energetics that drive the human power input. We are attempting to apply the same framework to the concept2 2000M time trials that our athlete undergo. ________________________________________________________________ We assumed that POWER would have been determined first and then the Virtual Boat PACE/Velocity derived using the equation you mentioned Power = 2.80 * Velocity (meters/sec)³ rearranged to Velocity = CubeRoot OF (Power / 2.80) (meters/sec) ________________________________________________________________ The answer we are seeking must ultimately center around the three metal discs passing a pickup on the spinning flywheel giving the PM3 linear velocity of the chain and angular velocity of the spinning wheel with a fixed known value of the Moment of Inertia of the Flywheel. Does anyone KNOW FOR SURE what the specific numeric equation(s) are that the PM3 is using to determine the POWER ? MarkA and MarkO

[old] tomhz · Post by **[old] tomhz** » May 18th, 2005, 6:30 am

<table border='0' align='center' width='95%' cellpadding='3' cellspacing='1'><tr><td><div class='genmed'>QUOTE(bbsportz @ May 17 2005, 01:39 AM)</div></td></tr><tr><td class='quote'> The answer we are seeking must ultimately center around the three metal discs passing a pickup on the spinning flywheel giving the PM3 linear velocity of the chain and angular velocity of the spinning wheel with a fixed known value of the Moment of Inertia of the Flywheel. Does anyone KNOW FOR SURE what the specific numeric equation(s) are that the PM3 is using to determine the POWER ? MarkA and MarkO </td></tr></table> That is right. I suggest you contact the people that created the software package <a href='http://www.ps-sport.net/ergmonitor.htm' target='_blank'>Ergmonitor</a>: Paul Smith and Mike Niezgoda. They know exactly how to calculate the power from the speed variations of the flywheel. Tom

[old] PaulS · Post by **[old] PaulS** » May 18th, 2005, 11:04 am

<table border='0' align='center' width='95%' cellpadding='3' cellspacing='1'><tr><td><div class='genmed'>QUOTE(tomhz @ May 18 2005, 02:30 AM)</div></td></tr><tr><td class='quote'><table border='0' align='center' width='95%' cellpadding='3' cellspacing='1'><tr><td><div class='genmed'>QUOTE(bbsportz @ May 17 2005, 01:39 AM)</div></td></tr><tr><td class='quote'> The answer we are seeking must ultimately center around the three metal discs passing a pickup on the spinning flywheel giving the PM3 linear velocity of the chain and angular velocity of the spinning wheel with a fixed known value of the Moment of Inertia of the Flywheel. Does anyone KNOW FOR SURE what the specific numeric equation(s) are that the PM3 is using to determine the POWER ? MarkA and MarkO </td></tr></table> That is right. I suggest you contact the people that created the software package <a href='http://www.ps-sport.net/ergmonitor.htm' target='_blank'>Ergmonitor</a>: Paul Smith and Mike Niezgoda. They know exactly how to calculate the power from the speed variations of the flywheel. Tom </td></tr></table> Between Anu and Marinus, the Marks should have everything they need, except for the very specific details regarding the segment during the recovery on which the Drag Factor calulation relies. C2 wouldn't tell us, so we had to make our best guess, and after a lot of trials we hit it pretty close (Times within 0.2% at 30 minutes, I've never had a variation of more than a single stroke.) Another concern is when to start the Timer, we start ours (ErgMonitor) considerably sooner than C2 does, but that's just because they chose to give a few more revs before starting. Cheers!